Abstract: This paper reports a study of Ba0.9Sr0.1TiO3 films deposited on Pt/Ti/SiO2/Si substrates. The annealing temperatures were 750°C, 850°C and 950°C. An increase of the average size of grains was observed, from 60 nm at 750°C to 110 nm at 950°C, as well as an increase of the dielectric constant, remnant polarization and tunability. When the annealing time was decreased from 1 hour to 15 min, the dielectric constant and remnant polarization values have been increased. The optimized annealing conditions (950°C for 15 min) give the following results: εr = 780 and tgδ = 0.01 at 100 kHz, Pr = 13 µC/cm², Ec = 63 kV/cm and a tunability of 55%.
Abstract: In this paper we present experimental results with the ion recombination process in the vapor phase growth method. We consider the growth process of only one element case, Zinc, because of the clarification of the change of electron states in the element, not the entropy effect due to different elements. The advantages of using the ion recombination process are the following; 1) controllability of total energy, 2) the highest quenching rate, 3) locality of the collision. The total energy of the ion system was below 240 eV. Zn- ions exist on the growth front surface and Zn+ ones impinge to the growth surface from the vapor phase. The crystal structures of deposited zinc films are measured with the XRD system. Very strong diffuse scattering intensity of x-ray diffraction was observed at 10 eV, 90 eV, 100 eV and 230 eV after seven months “annealing” in room temperature from the preparation. These experimental facts suggest the effectiveness of the application of the excitation process of the inner core electron system as a new advanced material process. In this process, the ion recombination process and the existence of a metastable state are essentially important factors.
Abstract: Aluminium Silicon reinforced with 50Vf% SiC has been produced by spontaneous infiltration at 900°C for 1 hour. Aluminium infiltrated preforms containing 1%wt Mg mixed with various of Si between 2 and 14wt%, as external dopant. However Al did not infiltrate a preform containing 1wt%Mg but if mixed with Si in the preform generated in more extensive infiltration. Effect of Si on characterisation of pure Al composites by spontaneous infiltration were studied and compared to Al-Si based matrix. Microstructural analysis of MMC as well as mechanical properties were also observed. It was found that increasing of Si content generated lower porosity thus increasing hardness due to aluminium could wet SiC preform well. Although the dopant was uniformly distributed throughout the perform but microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform as infiltration inwards from the top to the bottom of preform. The hardness of Al-Si composites is significantly increased with increasing of Si for both externally and internally doped system. This is associated with decreasing porosity with higher Si in composites.
Abstract: Steel wire rope – reinforced aluminium composite - has been developed to improve the ballistic properties and mobility of armour material. Critical to obtaining ballistic resistance is that the materials must be sufficiently hard and strong, especially at the surface where a projectile will first make impact. To obtain this resistance, aluminium alloys can be strengthened by adding Cu and Mg. This research studied the ballistic properties of aluminium composites with varied Cu and Mg content. The matrix used in this study was an Al-7Si master alloy with 0.08-1.03 wt. % Mg and 0.05-3.75 wt. % Cu, both independently and in combination. A high carbon steel wire rope was used as strengthening material. The samples were produced through the squeeze casting process with a pressure of 1 MPa at semi-solid melting temperatures of 590-610 °C. The slab was then rolled for 10 % reduction to increase the hardness. Ballistic testing was performed in accordance with ASTM F1233 by using a 9 mm calibre projectile and 900 direction. Micro structural observation was conducted in the as-cast and ballistic samples, performed with optical microscope and scanning electron microscope (SEM). The results showed that squeeze casting may improve interfacial wettability and reduce void. The increase in Mg resulted in the decline of interfacial voids, but Cu addition tended to increase them. The aluminium armour was able to withstand a 9 mm calibre projectile, although some cracks were visible. The wire rope was not effective in stopping the penetration of a 7.62 mm calibre projectile.
Abstract: The utilization of coconut fibers as reinforcement in polymer composites has been increase significantly due to their low cost and high specification of mechanical properties. Whereas kevlar fibers has widely used as the core material in flexible body armors due to its great mechanical properties, such as high strength, light weight, good chemical resistance and thermal stability. The research work is concerned with the evaluation of high speed impact and flexural test of hybrid textile reinforced epoxy composites. Samples were prepared from coir yarn, kevlar yarn, interlaced of coir and kevlar yarn with different warp/weft orientation and pure epoxy as control specimen. The woven samples were produced using handloom and the composites specimens were prepared using hand lay-up technique. From the results obtained, it was found that woven kevlar composites samples displayed the highest impact properties while it exhibits the lowest flexural properties. Results also showed that the composite plate for woven coir yarn (warp) and kevlar yarn (weft) has the flexural strength and impact strength of 17 MPa and 67 kJ/m², which presented as the nearest properties to woven Kevlar composite respectively. These results indicate that coir as a natural fiber can be used as a potential reinforcing material for high impact resistance such as body armors in order to reduce the usage of synthetic materials whilst utilizing the natural resources.
Abstract: Metallization techniques based on electroless coating are used to coat SiC particles reinforced to make Al-Si/SiC metal matrix composites. Nitric Acid (HNO3), aluminum powder and different percentage of magnesium addition were used in solutions as electroless coating medium to coat the surface of SiC particles. Five different percentage of Mg was used from 0.1 to 0.5 wt% in electrolyte solution. Metal oxide coating was characterised by scanning electron microscope (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) as well as Transmission Electron Microscope (TEM). It is obtained that metal oxide layer formed on the SiC surface was MgAl2O4 or spinel which was analysed by XRD and confirmed by EDS. Spinel (MgAl2O4) layer was found at all composition of Mg, and such layer improved wettability between SiC and Al-Si. It also is found that the solution with 0.2%wt Mg content generated more homogeneous metal oxide layer on SiC particles therefore the solution with 0.2wt% Mg was selected as electroless coating medium to coat SiC particles reinforced to produce Al-Si/SiC metal matrix composites by stir casting route. The phases present in Al-Si/SiC composites was spinel (MgAl2O4), Si eutectic and Mg2Si which was analysed by XRD.
Abstract: The phase and dissolution behavior of precipitates in biomedical ASTM F75 Co-Cr-Mo-C-Si-Mn alloys were investigated. Alloys of five different compositions, Co-28Cr-6Mo-0.25C-1Si, Co-28Cr-6Mo-0.25C-1Mn, Co-28Cr-6Mo-0.25C-1Si-1Mn, Co-28Cr-6Mo-0.15C-1Si, and Co-28Cr-6Mo-0.35C-1Si, were heat-treated from 1448 to 1548 K. The precipitates observed in the as-cast and heat-treated alloys were carbides (M23C6 type, h-phase, and p-phase) and an intermetallic compound (c-phase). The main precipitates observed after heat treatment at high temperatures such as 1548 K were p-phase and M23C6 type carbide. At these high temperatures, two types of starlike precipitates—dense and stripe-patterned—were observed. The starlike-dense precipitate was the p-phase, and the starlike precipitate with a stripe pattern was identified as the M23C6 type carbide and metallic fcc g-phase. In the alloys heat-treated at 1448 to 1498 K, blocky-dense M23C6 type carbide was primarily observed. c-phase was detected in the Co-28Cr-6Mo-0.15C-1Si alloy under as-cast condition and after heat treatment at 1448–1523 K for a short holding time. The addition of Si seemed to increase the holding time for complete precipitate dissolution because of the effects of Si on the promotion of p-phase formation at high temperatures and the increased carbon activity in the metallic matrix.
Abstract: The porous Hydroxyapatite (HA) ceramics have found enormous use in biomedical applications including bone tissue regeneration, cell proliferation, and drug delivery. This paper investigates the preparation and characterization of bovine Hydroxyapatite (BHA) porous bone graft by mixing sucrose powder as porogens with bovine bone powder. After uniaxially pressing at 156 MPa and pressurelessly sintering in air atmosphere at 1200°C for 2 hours the bioceramic showed an interconnecting porosity. The XRD analysis indicated that bovine hydroxyapatite (BHA) porous bone graft resulted in this research is single phase HA and is believed to be pure HA as indicated by the peak of the diffraction patterns (JCPDS 9-432). The phase analysis also shows that BHA porous bone graft is highly crystalline with domain crystallites sizes are between ~46 to ~99 nm (~4.6 to ~9.9 Å). Several trace elements in human bone such as titanium (Ti), iron (Fe), nickel (Ni), copper (Cu) and Zinc (Zn) were also detected in BHA porous bone graft as indicated by SR-XRF. This object is promising for bone regeneration because the interconnecting porosity in carbonated apatite provides a good environment for bone attachment and ingrowths
Abstract: In the general rule of casting design the thickest part of the cast should be placed near to the ingate. This arrangement was meant to guarantee the completion of filling process. An unusual vertical casting design to produce plates with different thicknesses was established based on the idea that the heat from molten metal will always warm up its entire runner. In this design the thinnest plate is placed near to the ingate. The design was made for producing thin wall ductile iron. This research was conducted to see the effects of reverse thickness arrangement in casting design to the microstructure and mechanical properties of the plates. Plates produced by this design were compared to plates produced by the same design with general casting arrangement. Thicknesses of the plates produced in this casting were 1, 2, 3, 4, and 5 mm. The moulds used were made from furan sand. Beside experiment, casting design simulation with Z-Cast was also conducted to ensure the completion of filling process and to see the manner of solidification. Casting simulation showed that arrangement of plates gave different filling and solidification manners. Although there were some differences, the filling was successful for both arrangements of plates. Skin effect was found in both designs. Nodule counts and nodularity were higher in the new design while average nodule diameters were lower. The result gained in tensile and hardness test did not follow the correlations in the characteristic of graphite. Mechanical properties showed that position of plate, ignoring the thickness, influence tensile strength and hardness.